Nitric oxide (NO) has been found to have an increasing number of biological roles including being a neurotransmitter. In a variety of these functions, it is known that NO is bound to heme proteins, but no detailed structural information is available on the nature of such binding. This project is aimed at using XAS data to understand the geometric and electronic structures of NO adducts of heme proteins. This structural information will also be used to gain a better understanding of how binding of NO activates the release of the NO-heme group from the heme protein.